Optical devices including assistant layers

ABSTRACT

A waveguide including a top cladding layer, the top cladding layer including a material having an index of refraction, n1; an assistant layer, the assistant layer positioned adjacent the top cladding layer, the assistant layer including a material having an index of refraction, n2; a core layer, the core layer positioned adjacent the assistant layer, the core layer including a material having an index of refraction, n3; and a bottom cladding layer, the bottom cladding layer positioned adjacent the core layer, the bottom cladding layer including a material having an index of refraction, n4, wherein n1 is less than both n2 and n3, n3 is greater than n1 and n4, and n4 is less than n3 and n2.

PRIORITY

This application claims priority to U.S. Provisional Application No.61/637,560 entitled “OPTICAL WAVEGUIDE FOR HEAT ASSISTED MAGNETICRECORDING” having docket number STL17225.01 filed on Apr. 24, 2012, thedisclosure of which is incorporated herein by reference thereto.

BACKGROUND

In thermally assisted magnetic/optical recording, information bits arerecorded to a storage layer of a storage media at elevated temperatures.Generally, a spot or bit on the storage medium is heated to reduce itscoercivity sufficiently so that an applied magnetic field or opticalwrite signal can record data to the storage medium. Current methods ofheating the storage media include directing and focusing energy onto thestorage media. Different and more advantageous methods and devices forfocusing the energy are needed in order to decrease the size of theheated spot in order to increase the storage density of the storagemedia.

SUMMARY

A waveguide including a top cladding layer, the top cladding layerincluding a material having an index of refraction, n1; an assistantlayer, the assistant layer positioned adjacent the top cladding layer,the assistant layer including a material having an index of refraction,n2; a core layer, the core layer positioned adjacent the assistantlayer, the core layer including a material having an index ofrefraction, n3; and a bottom cladding layer, the bottom cladding layerpositioned adjacent the core layer, the bottom cladding layer includinga material having an index of refraction, n4, wherein n1 is less thanboth n2 and n3, n3 is greater than n1 and n4, and n4 is less than n3 andn2.

A device including a magnetic pole; a near field transducer-heat sink(NFT-HS), the NFT-HS positioned adjacent the magnetic pole, the NFT-HShaving an air bearing surface and an opposing back surface; and awaveguide, the waveguide including a top cladding layer, the topcladding layer including a material having an index of refraction, n1;an assistant layer, the assistant layer positioned adjacent the topcladding layer, the assistant layer including a material having an indexof refraction, n2; a core layer, the core layer positioned adjacent theassistant layer, the core layer including a material having an index ofrefraction, n3; and a bottom cladding layer, the bottom cladding layerpositioned adjacent the core layer, the bottom cladding layer includinga material having an index of refraction, n4, wherein n1 is less thanboth n2 and n3, n3 is greater than n1 and n4, and n4 is less than n3 andn2, wherein the top cladding layer of the waveguide is positionedadjacent the magnetic pole and the back surface of the NFT-HS and theassistant layer of the waveguide is positioned adjacent the back surfaceof the NFT-HS.

Also disclosed is a device that includes a light source; and awaveguide, the waveguide including: a top cladding layer, the topcladding layer including a material having an index of refraction, n1;an assistant layer, the assistant layer positioned adjacent the topcladding layer, the assistant layer including a material having an indexof refraction, n2; a core layer, the core layer positioned adjacent theassistant layer, the core layer including a material having an index ofrefraction, n3; and a bottom cladding layer, the bottom cladding layerpositioned adjacent the core layer, the bottom cladding layer includinga material having an index of refraction, n4, wherein n1 is less thanboth n2 and n3, n3 is greater than n1 and n4, and n4 is less than n3 andn2, and wherein the waveguide is configured to receive light from thelight source and direct it out into the NFT-HS.

The above summary of the present disclosure is not intended to describeeach disclosed embodiment or every implementation of the presentdisclosure. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which examples can beused in various combinations. In each instance, the recited list servesonly as a representative group and should not be interpreted as anexclusive list.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an isometric view of a system including a disc drive.

FIG. 2 is a block diagram of a particular illustrative embodiment of arecording head including a waveguide in communication with anillustrative recording medium.

FIG. 3 is a partial cross section of a disclosed device.

FIG. 4 is a partial cross section of a disclosed device.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the properties sought tobe obtained by those skilled in the art utilizing the teachingsdisclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

“Include,” “including,” or like terms means encompassing but not limitedto, that is, including and not exclusive. It should be noted that “top”and “bottom” (or other terms like “upper” and “lower”) are utilizedstrictly for relative descriptions and do not imply any overallorientation of the article in which the described element is located.

Disclosed devices can offer the advantage of providing more efficienttransfer of energy from an energy source to the magnetic storage mediato be heated, a smaller focal point at the point of heating, or somecombination thereof. In some embodiments, disclosed devices can be usedwithin other devices or systems, such as magnetic recording heads, morespecifically, thermally or heat assisted magnetic recording (HAMR)heads, or disc drives that include such devices.

FIG. 1 is an isometric view of a disc drive 100 in which discloseddevices such as disclosed optical devices may be useful. Disc drive 100includes a housing with a base 102 and a top cover (not shown). Discdrive 100 further includes a disc pack 106, which is mounted on aspindle motor (not shown) by a disc clamp 108. Disc pack 106 includes aplurality of individual discs, which are mounted for co-rotation aboutcentral axis 109. Each disc surface has an associated disc head slider110 which is mounted to disc drive 100 for communication with the discsurface. In the example shown in FIG. 1, sliders 110 are supported bysuspensions 112 which are in turn attached to track accessing arms 114of an actuator 116. The actuator shown in FIG. 1 is of the type known asa rotary moving coil actuator and includes a voice coil motor (VCM),shown generally at 118. Voice coil motor 118 rotates actuator 116 withits attached heads 110 about a pivot shaft 120 to position heads 110over a desired data track along an arcuate path 122 between a disc innerdiameter 124 and a disc outer diameter 126. Voice coil motor 118 isdriven by servo electronics 130 based on signals generated by heads 110and a host computer (not shown).

In general, the disc head slider 110 supports a recording head that caninclude disclosed optical devices. Disclosed optical devices included inthe disc head slider 110 can be utilized to direct focused energy onto asurface of a disc 107 of the disc pack 106 to provide heat-assistedrecording. A control circuit included with the servo electronics 130 orco-located with the servo electronics 130 along a bottom portion of thedisc drive 100 may be used to control a position of the slider 110 andthe associated read/write head relative to one of the individual discs107 of the disc pack 106.

FIG. 2 is a block diagram of a particular illustrative embodiment of asystem 200 including a recording head 201 having an optical device 204such as those depicted herein. The system 200 includes a recordingmedium 210 located perpendicular to a Y-axis of the optical device 204.The recording head 201 includes an air-bearing slider 202 that fliesover the surface of the recording medium 210 and that is adapted to beadjusted in the X-direction and the Z-direction and that maintains afly-height over the surface of the recording medium 210 in theY-direction based on airflow. The air-bearing slider 202 is coupled to aread/write head 206, which is adjacent to the optical device 204. Theoptical device 204 focuses evanescent waves energy toward the surface ofthe recording medium 210. The recording head 201 can optionally includeovercoat layer 208 that functions to protect the read/write head 206.

In a particular embodiment, the optical device directs focused energy214 onto the surface of the recording medium 210 to heat a local area ofthe recording medium 210 to reduce a coercivity of the local area.Concurrently, the read/write head 206 directs a recording field 216 ontothe recording medium 210 in the heated local area to record data to therecording medium.

FIG. 3 shows a device 300. The device 300 can generally include awaveguide, or an optical waveguide 330. The waveguide 300 can include abottom cladding layer or structure 310, a core layer or structure 315, atop cladding layer or structure 325 and an assistant layer or structure320. The bottom cladding layer 310 can generally be positioned adjacentthe core layer 315. The assistant layer 320 can generally be positionedadjacent the core layer 315 and the top cladding layer 325. Statedanother way, the assistant layer 320 can be positioned between the corelayer 315 and the top cladding layer 325; the core layer 315 can bepositioned between the bottom cladding layer 310 and the assistant layer320. Generally, the waveguide 330 can also be described as a multilayerstructure that includes the bottom cladding layer 310, the core layer315, the assistant layer 320 and the top cladding layer 325.

The top cladding layer 325 generally includes or can be made of amaterial that has an index of refraction, n1. The assistant layer 320generally includes or can be made of a material that has an index ofrefraction, n2. The core layer 315 generally includes or can be made ofa material that has an index of refraction, n3. In some embodiments,discussed herein below, the core layer 315 can itself be a multilayerstructure. The bottom cladding layer 310 generally includes or can bemade of a material that has an index of refraction, n4.

Generally, the relationship of the indices of refraction of the variouslayers can be described in more detail. Generally, n1 is not greaterthan, and in some embodiments less than both n2 and n3; n1 can be lessthan, equal to, or greater than n4. Generally, n3 is not less than, andin some embodiments greater than both n1 and n4; n3 can be less than,equal to, or greater than n2. Generally, n4 is not greater than, and insome embodiments less than n3 and n2; n4 can be less than, equal to, orgreater than n1. In some embodiments, n2 can be not less than andoptionally greater than n1; n2 can be less than, equal to, or greaterthan n3; n2 can be not less than and optionally greater than n4.

The material of the core layer 315 may have a refractive index greaterthan the material of either or both of the bottom and top claddinglayers 310 and 325. This enables the core layer 315 to more efficientlytransmit the light energy or electromagnetic wave for heating therecording medium. In some embodiments, the material of the core layer315 may have a refractive index (n3) of about 1.9 to about 4.0. Incontrast, the material of the either or both of the bottom and topcladding layers 310 and 325 may have a refractive index of about 1.0 toabout 2.0. By forming the core layer 315 with a higher refractive indexthan the cladding layers, the core layer 315 is able to more efficientlyguide a propagating or guided electromagnetic planar waveguide mode bytotal internal reflection. In some embodiments, by increasing the ratioof the core layer 315 refractive index to the cladding layers'refractive index (for the refractive index ranges stated herein), theenergy of the propagating or guided mode can be more greatly confinedwithin the core layer 315. As used herein, the term propagating orguided electromagnetic planar waveguide mode generally refers to opticalmodes which are presented as a solution of the eigenvalue equation,which is derived from Maxwell's equations subject to the boundaryconditions generally imposed by the waveguide geometry.

In some embodiments, the bottom cladding layer 310 may be formed of amaterial such as, for example SiO₂, MgF₂, Al₂O₃, porous silica, orcombinations thereof. In some embodiments, the bottom cladding layer 310can be formed of a material that has advantageous properties, forexample, the material can have advantageous corrosion resistantproperties. Corrosion resistance can be important because the bottomcladding layer 310 is exposed to the air bearing surface (ABS) of thedevice. In some embodiments, the bottom cladding layer can be made ofSiO₂, for example. In some embodiments, the top cladding layer 325 maybe formed of a material such as, for example SiO₂, MgF₂, Al₂O₃, poroussilica, or combinations thereof. The top and bottom cladding layers canbe the same or different materials.

In some embodiments, the core layer 315 may be formed of a material suchas, for example, Ta₂O₅, TiO_(x), ZnSe, ZnS, Si, SiN , GaP, GaN, diamond,or combinations thereof. In some embodiments, the core layer 315 may beformed of a material such as, for example Ta₂O₅, SiN_(x), TiO_(x),diamond, or combinations thereof. In some embodiments, discussed below,the core layer 315 can be made of a multilayer structure.

In some embodiments, the assistant layer 320 may be formed of a materialsuch as, for example, SiON_(x), Yb₂O₃, Y₂O₃, Ta₂O₅ (TaO_(x)), TaSiO₂(TaSiO_(x)), Hf₂O₃, Nb₂O₃ (NbO_(x)), AlN, or combinations thereof. Insome embodiments, the assistant layer 320 may be formed of Y₂O₃, forexample.

The optical waveguide 330 can be positioned adjacent other structures,and in embodiments can be configured to work in connection with otherstructures or devices. The embodiment of the optical waveguide 330depicted in FIG. 3 is configured adjacent a magnetic pole 340, and anear field transducer-heat sink (NFT-HS).

In some embodiments, the core layer 315 may have a thickness, in the zdirection (see FIG. 3), of 20 nm to 500 nm. The bottom cladding layer310 may have a thickness in the z direction, of 200 nm to 2000 nm. Thebottom cladding layer 310 should be sufficiently thick such that theelectric field from the propagating waveguide mode does not extendappreciably beyond the bottom cladding layer 310 and thereby interactwith any materials or structure outside of the waveguide 330. In someembodiments, increasing the ratio of the core layer 315 thickness to thebottom cladding layer 310 thickness (for the thickness ranges statedherein), the energy of the propagating mode can be more greatly confinedwithin the core layer 315.

In some embodiments, the thickness of the assistant layer 320 can bedependent on other structures positioned adjacent the assistant layer,adjacent the waveguide 330, or a combination thereof. The thickness ofthe top cladding layer 320 can be dependent on other structurespositioned adjacent the assistant layer, adjacent the waveguide 330, ora combination thereof

The device 300 depicted in FIG. 3 includes not only an optical waveguide330, but also a near field transducer-heat sink (referred to herein asNFT-HS) 335 and a magnetic pole 340. The NFT-HS can be a singlestructure that functions as both a near field transducer and a heat sinkor it can be a multi-part structure which as a whole functions as a nearfield transducer and a heat sink. In some embodiments, the NFT-HS can bea peg/disc type of NFT, which can also be referred to as a lollipopstructure, a gap type of NFT, or a funnel-type NFT for example. The nearfield transducer function of the NFT-HS functions to condense incominglight rays to a location on the magnetic media disc 305, while the heatsink function of the NFT-HS functions to funnel heat, which is generatedby the NFT function, away from the NFT structure. The NFT-HS 335 can bedescribed as having an air bearing surface 337. The air bearing surface337 is adjacent the magnetic media disc 305. The NFT-HS 335 also has aback surface 339, which is the opposite or opposing surface as the airbearing surface 337. The magnetic pole 340 can generally function as awrite pole in a read-write head. Although the examples discussed hereindepict perpendicular magnetic recording heads, it will be appreciatedthat the embodiments depicted herein may also be used in conjunctionwith other types of recording heads and/or storage media where it may beuseful to employ heat assisted magnetic recording.

The location of some of the components of the waveguide 330 can befurther described with respect to the location of the NFT-HS 335 and themagnetic pole 340. The position of the top cladding layer 325 can bedescribed as being positioned adjacent the back surface 339 of theNFT-HS 335. The positioned of the top cladding layer 325 can also bedescribed as being positioned adjacent the magnetic pole 340. In someembodiments, the top cladding layer 325 can extend beyond (in the zdirection) the magnetic pole 340. In some embodiments, the top claddinglayer 325 can at least fill a region defined by the assistant layer 320,the back surface 330 of the NFT-HS 335 and the magnetic pole 340. Insuch embodiments, the thickness of the top cladding layer 325 wouldtherefore be defined, or limited by the structures surrounding it. Theposition of the assistant layer 320 can also be further described withrespect to the location of the NFT-HS 335. The position of the assistantlayer 320 can be described as being positioned adjacent the back surface330 of the NFT-HS 335.

The thickness of the assistant layer 320 and the top cladding layer 325can also be described with respect to adjacent structures. For example,if the NFT-HS is described as having a height (in the z direction, orstated another way, parallel to the ABS), the thickness of the assistantlayer 320 (in the z direction) can be described with respect to theheight of the NFT-HS. In some embodiments, the assistant layer 320 has athickness that is not greater than half the height of the NFT-HS. Insome embodiments, the assistant layer 320 can have a thickness that isless than half the height of the NFT-HS. In some embodiments, a NFT-HScan have a height of 200 nm. In such embodiments, the assistant layer320 can have a thickness of not greater than 100 nm. In someembodiments, the assistant layer 320 can have a thickness from 40 nm to80 nm.

The inclusion of the assistant layer in disclosed optical waveguides canfunction to push the waveguide mode field into the NFT. When usingconfigurations such as those disclosed herein, the field will decayquickly away from the top cladding layer, thereby lowering lightabsorption in the NFT-HS and magnetic pole. Lower light absorptionresults in a lower temperature rise and concomitant enhancedreliability. Disclosed waveguides can also allow the NFT to be tuned atthe resonance in the environment of the assistant layer where the bottompart and peg (in the embodiment of a lollipop type NFT) is immersed,which can contribute to the energy transfer to the magnetic media. Thetop part of the NFT is immersed in the top cladding layer, where the NFTis off resonance. Such an arrangement can force the plasmonic surfacewave to be efficiently generated in the bottom part of the NFT and befunneled to the peg. The lower field (off-resonance) in the top reducesthe light absorption in the NFT and also the magnetic pole behind it.The use of the assistant layer in combination with the top claddinglayer can also be effective to reduce the absorption in the magneticpole outside the NFT region, where transversely polarized solidimmersion mirrors (SIMs) exist.

The device depicted in FIG. 3 also includes a light source 345. Thelight source 345 is configured to generate light, which is directed intothe optical waveguide 330. More specifically, the light source 345 andoptical waveguide 330 are configured so that light from the light sourceis received by the waveguide and directed out the waveguide into theNFT-HS. Other devices and structures not depicted herein could beutilized to direct the light from the light source 345 into the opticalwaveguide 330. Exemplary types of structures or devices can include, forexample, solid immersion mirrors including parabolic mirrors forexample, mode index lenses, and three-dimensional channel waveguides.Exemplary types of light sources can include, for example laser diodes,light emitting diodes (LEDs), edge emitting laser diodes (EELs),vertical cavity surface emitting lasers (VCSELs), and surface emittingdiodes.

FIG. 4 depicts an embodiment of a device 400 that includes a core layer415 that includes more than one layer. Such a laminated core layer 415can be referred to as a laminated core layer. In such a laminated corelayer, the lower core layer 417 includes a material with a lower indexof refraction (relative to the upper core layer) and is adjacent thebottom cladding layer 410 and an upper core layer 419 includes amaterial with a higher index of refraction (relative to the lower corelayer) and is adjacent the assistant layer 420. Such a waveguide 430 canalso include a top cladding layer 425. The disclosed device alsoincludes a NFT-HS 435 and a magnetic pole 440.

The magnetic media 405 is also illustrated in FIG. 4. Example oflaminated core layers can be found in commonly assigned U.S. patentapplication Ser. No. 13/454,999, entitled “LAYERED OPTICAL WAVEGUIDE ANDNEAR FIELD TRANSDUCER”, filed on Apr. 24, 2012, having docket numberSTB.024.A1, the disclosure of which is incorporated herein by referencethereto.

The present disclosure is illustrated by the following examples. It isto be understood that the particular examples, assumptions, modeling,and procedures are to be interpreted broadly in accordance with thescope and spirit of the invention as set forth herein.

EXAMPLES

To demonstrate a disclosed optical waveguide, various waveguides andcomparative waveguides were modeled. A comparative waveguide (C1)included a 125 nm thick Ta₂O₅ core layer having an index of refraction,n=2.08; top and bottom cladding layers of Al₂O₃ having an index ofrefraction, n=1.65; a lollipop NFT composed of a gold (n=0.188+j 5.39)peg (peg dimension=40 nm along×direction−cross track; by 32 nm along zdirection−down track) and disc (cylinder diameter 200 nm); and a slopedFeCo magnetic pole (n=3.17+j 3.95) located behind (a strip 250 nm widealong the x direction and 100 nm high along the z direction, sloped at26.56° from the x direction). The NFT-pole spacing on the air bearingsurface was 20 nm. The media consisted of a 12.6 nm thick Fe layer(n=2.94+j 3.41), a 10 nm MgO layer (n=1.70) and a 60 nm Cu layer(n=0.26+j 5.29) on a glass substrate (n=1.50). The light wavelength invacuum λ=830 nm.

Another comparative waveguide (C2) was exactly the same as C1, butreplaced the bottom cladding layer with SiO₂. This was intended to pushthe field into the top cladding layer. A first exemplary disclosedwaveguide (Ex. 1) was exactly the same as C2 except that the topcladding layer was replaced with a top cladding layer-assistant layerstructure. The assistant layer structure was 70 nm thick Y₂O₃ with anindex of refraction, n=1.80. A second exemplary disclosed waveguide (Ex.2) was exactly the same as Ex. 1 except that the Al₂O₃ top cladding wasreplaced with SiO₂.

Table 1 shows the results of modeling. CE50 is the light absorption inthe Fe layer in a footprint of 50 nm by 50 nm. The absorption includesthe total absorption in the NFT and magnetic pole. The FOM (figure ofmerit) is defined as the CE50/absorption, which is a measure of headsperformance.

TABLE 1 CE Waveguide relative FOM CE₅₀ Absorption structure C1

1    0.082 0.0115 0.14  Al₂O₃/Ta₂O₅/ Al₂O₃ C2

1.19  0.074 0.0137 0.185 SiO₂/Ta₂O₅/ Al₂O₃ Ex. 1

1.626 0.099 0.0187 0.189 SiO₂/Ta₂O₅/Y₂O₃ (n = 1.80, 70-nm thick)/ Al₂O₃Ex. 2

1.748 0.122 0.0201 0.164 SiO₂/Ta₂O₅/Y₂O₃ (n = 1.80, 70-nm thick)/ SiO₂

As seen from Table 1, all of C1, Ex. 1 and Ex. 2 have better NFTefficiency that C1. One cause for this improvement is the replacement ofthe Al₂O₃ bottom cladding with SiO₂. This pushes the field into the topcladding layer. Ex. 1 and 2 have even better NFT efficiency, due to theaddition of the assistant layer structure of the high index Y₂O₃. C2 hasbetter CE50, but a poorer FOM, which is generally not desired. Theassistant layer improves both the NFT efficiency and the figure of merit(FOM). Ex. 2 has an efficiency improvement of about 1.8 times and afigure of merit (FOM) improvement of about 1.5 times.

NFT efficiency could be further improved by using a multilayer core. Anexample of such a multilayer core would be a bilayer of Ta₂O₅ and TiO₂.The Ta₂O5 has a lower index of refraction than the TiO2, further pushingthe field into the top cladding layer, thereby increasing NFTefficiency. However, the figure of merit (FOM) may not becorrespondingly improved. A specific example would be the same as Ex. 2,but replacing the core layer with a bi layer of 40 nm thick Ta₂O₅ and 40nm thick TiO₂ (n=2.30). The CE relative=2.226, but the figure of merit(FOM)=0.119, which is lower than Ex. 2 in Table 1.

Thus, embodiments of optical devices including assistant layers aredisclosed. The implementations described above and other implementationsare within the scope of the following claims. One skilled in the artwill appreciate that the present disclosure can be practiced withembodiments other than those disclosed. The disclosed embodiments arepresented for purposes of illustration and not limitation.

1-20. (canceled)
 21. A waveguide comprising: a top cladding layer, thetop cladding layer comprising a material having an index of refraction,n1; an assistant layer, the assistant layer positioned adjacent the topcladding layer, the assistant layer comprising a material having anindex of refraction, n2; a core layer, the core layer positionedadjacent the assistant layer, the core layer comprising a lower corelayer having a lower core layer index of refraction and an upper corelayer having an upper core layer index of refraction, wherein the uppercore layer is adjacent the assistant layer and; and a bottom claddinglayer comprising a material having an index of refraction, n4, andwherein the lower core layer is positioned adjacent the bottom claddinglayer wherein n1 is less than n2, and n4 is less n2.
 22. The waveguideaccording to claim 21, wherein the lower core layer index of refractionis less than the upper core layer index of refraction.
 23. The waveguideaccording to claim 22, wherein both the lower core layer index ofrefraction and the upper core layer index of refraction are higher thann1 and n4.
 24. The waveguide according to claim 21, wherein the lowercore layer Ta₂O₅ and the upper core layer comprises TiO₂ or Nb₂O₅. 25.The waveguide according to claim 21, wherein the core layer furthercomprises a middle layer positioned between the lower core layer and theupper core layer.
 26. The waveguide according to claim 21, wherein theassistant layer has a thickness from about 40 nm to about 80 nm.
 27. Thewaveguide according to claim 21, wherein the assistant layer comprisesSiON_(x), Yb₂O₃, Y₂O₃, Nb₂O₃, AlN, Al₂O₃, or combinations thereof. 28.The waveguide according to claim 21, wherein the assistant layercomprises Y₂O₃.
 29. The waveguide according to claim 21, wherein the topcladding layer comprises SiO₂, Al₂O₃, MgF₂, porous silica, orcombinations thereof.
 30. The waveguide according to claim 21, whereinthe top cladding layer comprises SiO₂, the assistant layer comprisesY₂O₃, and the bottom cladding layer comprises SiO₂.
 31. An apparatuscomprising: a magnetic pole; a near field transducer-heat sink (NFT-HS),the NFT-HS positioned adjacent the magnetic pole, the NFT-HS having anair bearing surface and an opposing back surface; and a waveguide, thewaveguide comprising: a top cladding layer, the top cladding layercomprising a material having an index of refraction, n1; an assistantlayer, the assistant layer positioned adjacent the top cladding layer,the assistant layer comprising a material having an index of refraction,n2; a core layer, the core layer positioned adjacent the assistantlayer, the core layer comprising a lower core layer having a lower corelayer index of refraction and an upper core layer having an upper corelayer index of refraction, wherein the upper core layer is adjacent theassistant layer and; and a bottom cladding layer comprising a materialhaving an index of refraction, n4, and wherein the lower core layer ispositioned adjacent the bottom cladding layer wherein n1 is less thann2, and n4 is less n2, wherein the top cladding layer of the waveguideis positioned adjacent the magnetic pole and the back surface of theNFT-HS and the assistant layer of the waveguide is positioned adjacentthe back surface of the NFT-HS.
 32. The apparatus according to claim 31,wherein the NFT-HS has a height parallel to its air bearing surface, anda thickness of the assistant layer is not greater than half the heightof the NFT-HS.
 33. The apparatus according to claim 32, wherein theNFT-HS has a height of about 200 nm.
 34. The apparatus according toclaim 33, wherein the assistant layer has a thickness of not greaterthan about 100 nm.
 35. The apparatus according to claim 33, wherein theassistant layer has a thickness from about 40 nm to about 80 nm.
 36. Theapparatus according to claim 30, wherein the top cladding layercompletely fills a region defined by the back surface of the NFT-HS, theassistant layer and the magnetic pole.
 37. A device comprising: a lightsource; and a waveguide, the waveguide comprising: a top cladding layer,the top cladding layer comprising a material having an index ofrefraction, n1; an assistant layer, the assistant layer positionedadjacent the top cladding layer, the assistant layer comprising amaterial having an index of refraction, n2; a core layer, the core layerpositioned adjacent the assistant layer, the core layer comprising alower core layer having a lower core layer index of refraction and anupper core layer having an upper core layer index of refraction, whereinthe upper core layer is adjacent the assistant layer and; and a bottomcladding layer comprising a material having an index of refraction, n4,and wherein the lower core layer is positioned adjacent the bottomcladding layer wherein n1 is less than n2, and n4 is less n2, andwherein the waveguide is configured to receive light from the lightsource and direct it out into the NFT-HS.
 38. The device according toclaim 37, wherein the light source is a laser diode, a light emittingdiode (LED), an edge emitting laser diode (EEL), a vertical cavitysurface emitting laser (VCSEL), or a surface emitting diode.
 39. Thedevice according to claim 37, wherein the top cladding comprises SiO₂,MgF₂, Al₂O₃, porous silica, or combinations thereof; the assistant layercomprises SiON_(x), Yb₂O₃, Y₂O₃, NbO_(x), AlN, Hf₂O₃, TaSiO_(x),TaO_(x), Al₂O₃, or combinations thereof the core layer comprises Ta₂O₅,SiN_(x), ZnS, TiO_(x), diamond, or combinations thereof; and the bottomcladding layer comprises SiO₂, MgF₂, Al₂O₃, porous silica, orcombinations thereof
 40. The device according to claim 37, wherein thetop cladding layer comprises SiO₂, the assistant layer comprises Y₂O₃,and the bottom cladding layer comprises SiO₂.